1. Field of the Invention
The present invention relates generally to a motor particularly suitable for use in an automotive air-conditioner for driving a blower, and more particularly to a magnetizing pattern of a rotor magnet of the motor and a method of magnetizing the rotor magnet.
2. Description of the Prior Art
A conventional rotor magnet known from Japanese Utility Model Laid-open Publication No. 61-114979 has a magnetizing pattern composed of a rectangular waveform-like magnetic flux density distribution pattern, such as shown in FIG. 5(a), which is formed by magnetizing the adjacent magnets to have a constant magnetic force. According to another known rotor magnet disclosed in Japanese Utility Model Laid-open Publication No. 62-152695, the magnets are magnetized so as to form a substantially sinusoidal (but not continuous) waveform-like magnetic flux distribution pattern, such as shown in FIG. 6(a), in which each magnet has a maximum magnetic force at the center and gradually decreases toward the opposite ends thereof.
When using the rotor magnet having the rectangular waveform-like magnetic flux density distribution pattern, the magnetic polarity changes abruptly as shown in FIG. 5(b) and generates objectionable vibration which causes resonance vibration of the motor and a case containing the motor, thereby enhancing the operation noise of the motor.
On the other hand, the rotor magnet having the substantially sinusoidal waveform-like magnetic flux density distribution pattern produces a distortion each time the magnetic polarity changes during rotation of the motor, as shown in FIG. 6(b). The operation noise of the motor cannot be further reduced.